Elastic-wave-based synthetic aperture focusing technique imaging system for detecting voids inside concrete structures

Abstract

In this paper, an elastic-wave-based imaging system was proposed for adopting synthetic aperture focusing technique to reveal the voids inside concrete structures. Design concept of each component in this system, including an impact source generator, a transducer, a signal capturing unit, and operation software, is clearly described. Relation between contact time and impact source selection was discussed and verified by an experiment of steel ball free-falling on a concrete specimen. A displacement transducer and corresponding signal capturing unit were carefully designed to get higher quality signals for Synthetic aperture focusing technique processing. A calibration experiment was conducted to ensure the capability of proposed point-source/point-receiver scheme for proper elastic wave generation and receiving. Besides, a concrete slab with an artificial defect was cast for experiment for usability evaluation. A 2D plane-stress finite difference simulation on corresponding numerical module was carried out for comparison. The experimental result shows good agreement with the numerical result not only on the B-scan diagram but also on the resultant image. It exhibits the potential of the proposed imaging system in inspecting defects of in-situ concrete structures by image.

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